1. Field of the Invention
The present invention generally relates to ink jet printhead apparatus and more particularly relates to apparatus for operatively interconnecting an ink jet printhead to an electrical power supply source used to control and piezoelectrically drive the printhead.
2. Description of Related Art
A piezoelectrically actuated in jet printhead is a relatively small device used to selectively eject tiny ink droplets onto a paper sheet operatively fed through a printer, in which the printhead is incorporated, to thereby form from the ejected ink droplets selected text and/or graphics on the sheet. In one representative configuration thereof, an ink jet printhead has a horizontally spaced parallel array of internal ink-receiving channels. These internal channels are covered at their front ends by a plate member through which a spaced series of small ink discharge orifices are formed. Each channel opens outwardly through a different one of the spaced orifices.
A spaced series of internal piezoelectric wall portions of the printhead body separate and laterally bound the channels along their lengths. To eject an ink droplet through a selected one of the discharge orifices, the two printhead sidewall portions that laterally bound the channel associated with the selected orifice are piezoelectrically deflected into the channel and then returned to their normal undeflected positions. The driven inward deflection of the opposite channel wall portions increases the pressure of the ink within the channel sufficiently to force a small quantity of ink, in droplet form, outwardly through the discharge orifice.
The electrical signals required to create and control the requisite printhead channel side wall deflections are typically generated by a suitable electronic driver. Due to the large number of very closely spaced ink channels present in even a small ink jet printhead structure, the resulting number of these electrical signals is quite high, while the physical area available at each ink channel for making the necessary printhead/driver connection is quite small. Accordingly, the connection of the printhead to its associated electronic driver has typically presented a significant connectivity design challenge.
One approach to this connectivity problem has been to mount the electronic driver directly on the printhead body with accompanying circuitry to eliminate the need for a large number of interconnects from the printhead structure to the overall ink jet printing system. This approach, however, undesirably results in a very substantial increase in the overall cost of the printhead structure which in many designs is a disposable unit.
Another approach to this connectivity problem has been to mount the electronic driver remotely from the printhead and provide the requisite electrical connections from the printhead channel side walls to the remotely disposed driver. One method previously proposed for providing this printhead-to-driver interconnect structure has been to form a high density, parallel array of electrically conductive surface traces on the printhead body and use a specially designed flexible ribbon connector to form the connection between these high density traces and a much lower density parallel array on a printed circuit board associated with the driver.
Under this method, the flexible connector has formed thereon a high density series of electrically conductive surface traces registrable with the traces on the printhead body, a low density series of electrically conductive surface traces registrable with corresponding traces on the driver circuit board, and a trace "fan-out" section interconnecting the high and low density connector traces. In actually forming the printhead-to-driver interconnection the high and low density trace sections on the flexible connector are respectively soldered (using a pressure/heat fellow process) to the high density trace section on the printhead body and to the low density trace section on the driver circuit board.
Despite this rather straightforward approach to electrically interconnecting the printhead to an associated electronic driver, the use of a flexible ribbon connector in this manner also greatly increases the cost associated with the overall printhead/driver system. Because of the significant pitch transition required in the flexible connector (a representative transition being from about a 3 mil pitch to about a 50 mil pitch), the cost of the specially designed flexible connector can substantially exceed the cost of the printhead structure with which it is used.
In view of the foregoing it can readily be seen that it would be desirable to provide improved high density interconnect apparatus for electrically connecting an ink jet printhead to a separate electronic driver associated therewith. It is accordingly an object of the present invention to provide such high density interconnect apparatus.